CA2160346C - Improved pressure decanter - Google Patents
Improved pressure decanterInfo
- Publication number
- CA2160346C CA2160346C CA002160346A CA2160346A CA2160346C CA 2160346 C CA2160346 C CA 2160346C CA 002160346 A CA002160346 A CA 002160346A CA 2160346 A CA2160346 A CA 2160346A CA 2160346 C CA2160346 C CA 2160346C
- Authority
- CA
- Canada
- Prior art keywords
- feedwell
- vessel
- solids
- section
- liquid
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D21/00—Separation of suspended solid particles from liquids by sedimentation
- B01D21/01—Separation of suspended solid particles from liquids by sedimentation using flocculating agents
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D21/00—Separation of suspended solid particles from liquids by sedimentation
- B01D21/02—Settling tanks with single outlets for the separated liquid
- B01D21/04—Settling tanks with single outlets for the separated liquid with moving scrapers
- B01D21/06—Settling tanks with single outlets for the separated liquid with moving scrapers with rotating scrapers
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D21/00—Separation of suspended solid particles from liquids by sedimentation
- B01D21/24—Feed or discharge mechanisms for settling tanks
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D21/00—Separation of suspended solid particles from liquids by sedimentation
- B01D21/24—Feed or discharge mechanisms for settling tanks
- B01D21/2427—The feed or discharge opening located at a distant position from the side walls
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D21/00—Separation of suspended solid particles from liquids by sedimentation
- B01D21/30—Control equipment
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D21/00—Separation of suspended solid particles from liquids by sedimentation
- B01D21/30—Control equipment
- B01D21/34—Controlling the feed distribution; Controlling the liquid level ; Control of process parameters
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Treatment Of Sludge (AREA)
- Centrifugal Separators (AREA)
- Paper (AREA)
- Separation Of Suspended Particles By Flocculating Agents (AREA)
Abstract
An apparatus for separating solids suspended in incoming pressurized liquid slurry is disclosed. The apparatus comprises a vessel having an elongated cylindrical vessel wall, a closed upper end and a bottom section for accumulation of solids. The vessel includes a stirrer mounted for rotation along an inside surface of the bottom section and a discharge spool mounted beneath the bottom section including at least one opening. An underflow pump is provided for discharging separated solids without loss of pressure in the apparatus. The apparatus further includes means for detecting solids level in the apparatus which preferably operates without distributing settling of the solids therein. Also, the apparatus includes a feedwell for receiving an incoming pressurized slurry stream, the feedwell having an opening a predetermined distance above a level in the apparatus defined by settled solids.
Description
WO 94126383 ~ ~ ~ ~ ~ PCTICA94100246 IMPROVED PRESSURE DECAN7.'ER
Technical Field This invention relates to an apparatus and process for separating solids from liquid under pressure and more particularly to a pressurized decanter system for separating red mud from Bayer process liquor without need to depressurize the slurry.
Background Art The Bayer process, now more than 100 years old, extracts alumina from bauxite ore by contacting crushed or p~slverized bauxite with a hot solution of caustic soda, whose concentration of rdaOH is usually expressed as equivalent Na2C03, to di;asolve the aluminum hydroxides conta:.ined therein as sodium aluminate. This solution of high sodium aluminate concentration is called pregnant liquor. The remaining undigested insoluble residue, known as red mud, is separated from the solution, usually by filtration or sedimentation or both.
Red mud typically includes large quantities of finely divided solids resistant: to separation. Alumina manufacturing therefore creates a need for improved separation systems, particularly those that can rapidly separate large quantitiess of slurries in an efficient manner.
In this connection,. some preliminary attempts appear to have been made to use. pressurized settling devices in clarifying finely divided solids from slurries. U.S.
Patent No. 2,107,919 (Turner) appears to discuss a pressure digester placed between two blow off tanks. U.S.
Patent No. 4,994,244 (Fulford) states that separation of ra_d mud from the digested slurry can be carried out at a temperature below the boiling atmospheric temperature of t:he liquor phase of the slurry. U.S. Patent No. 5,080,803 (:Bagatto) discusses a process and apparatus for decanting suspensions at and above' the atmospheric boiling point of t:he suspension. The apparatus operates at atmospheric pressure.
21fi034~
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.. .. . .. . . . . . ..
... . . . . . . ....
. . . . . . ...
. .. .
.".. .... 2 .. .. .. ...
While the foregoing references discuss attempts to increase separation efficiency of finely divided solids from slurries, there exists a need, particularly in the aluminum industry, for improved systems to carry out separation at high pressure and temperature.
Disclosure of the Invention The present invention relates to both an apparatus and process for separating solids suspended in an incoming pressurized liquid s7_urry.
The apparatus of: the invention includes an elongated, upright vessel of generally circular cross-section having a closed top end and a bottom sump for accumulating solids. A feedstock inlet is provided for feeding a liquid slurry into the vessel and a f~occulant injector is provided for injecting flocculant into the liquid slurry feedstock. The vesseal also_includes an outlet for discharging clarified liquid in an upper region thereof and an outlet in the bottom sump for drawing off separated solids. Other featui:es of the vessel include a means for detecting the Ieve:L of thickened slurry bed in the vesse'~.
and a raking/dewater:_ng device for slurry extending into the bottom sump.
In accordance w::th the present invention, the apparatus of above t;rpe is specia'~ly adapted for use in carrying out separat:_on at high pressure and temperature.
This includes a feedstock inlet system for receiving pressurized liquid s:.urry including an elongated cylindrical feedwell mounted axially in an upper region. of the vessel with an annular space between the feedwell and vessel wall, this feedwell having an open bottom, an opening in an upper region thereof and a feed inlet for the liquid slurry .Located in a side wall of the feedwell between the open bottom and upper opening.
The feedstock inlet into the feedweil is located a distance above the open bottom of the feedwell su~f'_cient to permit substantia:: f'~occulation of so'_ids and clarification of liqmid within the =eedwe_'~. Also, the AMENDED S~=~ ~
~1603~v oven bottom of the feeciwell v~s positioned above the surface of a thickened Slurry bed in the vesse~ a c=stance suffic=ent to permit c=_arified liquid emerg-~ng downwardlv from the bottom of the feedweil to separate _rom the floccu'~ated solids and travel upwardly in the annular ,,, space between t~:e feedwell and vesse'~ wa_ls to discharge through the upper outlet without substantially disturbing the thickened slurry bead. The outlet for discharging clarified liquor is adapted to operate under pressure, as is the outlet in the bottom of the sump.
Preferably the upper opening in the feedwell is located to permit a po._ti on of t:~e clan ified 1 i quid travelling upwardly th:=ough the annular space to enter the feedwell through the ot~ening in such a manner as to 1S provide an inverted chimney effect within the feedwell.
Thus ) the- portion of c l ar;~.fied l,;quid~ entering the- upper opening of the =eedwei:'_ _ravels downwardly through the f°eClWe l 1, mlX;ng Wlr..~_ <3n(~ dllllt~ng .'.:ie _:'lCOmlilg ~~?eC
si~r=y Wnlc.~. d=QS _~CCCL:latl0n. The upper Open;:lg 31SC
permits t:~e dvsengageme~nt of the accumulation of gas bubbles that would of:~e~r~rise hinder flocculation. anti settling.
The pressurized liquid slurry being fed tc t:~~e apparatus normally has a flocculant incorporated therei_~.
and this floccuiant is typically added by way of at least one injector mounted within an inlet pipe connected to the feed inlet of the feed~Nell. Typically, two injectors are used, the first being :Located adjacent the feed inlet of the feedwell and the second injector being located upstream from the first injector.
The elongated, upright pressure vessel of the invention is typically a cylindrical vessel of substantially uniform ~~ross-section. ~iowever, according to an alternative embodiment of this invention _~ is possible to use a vessel having a lower sector. of ~;arger cross-section: and a cylindrical upper sec~ior_ of sma'_~er cross-section.. __ is, cf course, necessary to have as ~~ow AMCi'JG~:: :~;; ;c=T
,_ as practical an averag~=_ upflow velocity of the separating clarified ,_i~uv-d i~ th~= zone v~.n which the flocculated soli ds are separating and fal~.ng downwardly =rom t:~e S lower end of the f?edw=11 toward the bed of thickened slurry, t:zereby hindering the downward passage of the solids as _y..t=a as possible. For t:zis reason, the vessel Ar'~~~~ c~
"'~ = 1 WO 94126383 216 0 3 4 ~ PCTlCA94100246 must have a relatively large diameter in this portion of its height. On the other hand, the portion of the vessel extending above the lower end of the feedwell does not have this velocity restriction and it has quite surprisingly been found that very clear overflow liquids containing as little as 25 mg/1 suspended solids can be obtained even in cases where the average upflow velocity of the separated liquid in the annular space between the feedwell and vessel is 20 to 25 m/h or higher. For this reason, the diameter of the upper portion of the pressure vessel can be considerably smaller than the lower portion of the vessel.
This provides important advantages in substantially lowering the costs of material for a pressure vessel and, furthermore, the relatively high velocity of the liquid travelling upwardly through the annular space between the vessel wall and feedwell considerably decreases scaling of the surfaces of the vessel.
The lower portion of larger cross-section can be spherical in shape or it may be in the form of a low, relatively fat cylinder with upper and lower conical portions, or a polyhedron, or a combination of these shapes. Preferably the maximum diameter of the lower section is at least 1.75 times the diameter of the smaller upper section.
The means for detecting the level of the thickened slurry bed within the vessel is preferably in the form of a series of pressure dif:Eerential detectors mounted in the cylindrical wall of the vessel. It is important that these not interfere with the settling of the thickened slurry bed and therefore should protrude as little as possible into the interior of the vessel.
Brief Description of the Drawincts FIG. 1 is a front view in section of the improved pressure decanter of the present invention.
FIG. 2 is a sectional view, partially broken away, of the improved pressure decanter of FIG. 1, taken along '~1603~~
line 2-2 i-~. - =G. 1.
- r. ,_ r ~ . _ ~ ,~ _ . = a r-a r 4, ~~ a _ m:. 3 .S a S_.__..OYla, ~__w ~;L t~lE'_ mDrJV~.~. C_ SSLi__ decanter of FI,~. _ taken along line _-3 in ~=G. _.
FIG. a is a schematic representation o~ a mounting ,, 3 for a _eve'_ indicator i_or vsse in the =mproved pressure decanter of ~TG~ ~.
FIG. 5 is a schc=matic representatior_ of an alternative corm of decanter vessel.
FIG. o' is a schematic representation of a still further form oz decanter vessel, and FIG. 7 is a graphical representation of settling in the improved pressure decanter of F.IG. _ measured 'revel detectors.
3est Modes =or Ca=rvi~cz Out =he =nvent~.or_ FIGS. 1-~ illustrate a preferred embodiment .~.L the pressure decanter-of the present invention Generally designated with the =e_erence number 10 '.'he pressure decanter 10 genera l ly :_nc l udes a cylindr ical pressur a vessel 12, a cr°_=°_ra.bl~r conical ~cttom sectior_ ';4, a closed upper end 15, a deep =eedwell 18 =or incoming pressurized slurry, and a sump 20 below the 'onical bottom section 14 to facilitate removal of solids under pressure from the decanter '~0. It also has ar_ upper out';et 39 _or discharging clariLied :Liquid under pressure. =urthermore, it includes a raking/d~~watering device 2inside the bottom section 14, a p.Lurality of mud level detectors 24 to determine the level of settled solids. The vessel 10 stands generally upri ght as shown in FIG . _ ar_d i s supported by legs 28.
The cylindrical pressure vessel 12 has an elongated cylindrical vessel wall of suf~icient strength and thickness to withstand t:~e pressures, temperatures and corrosiveness of the c~~ntents such as pressurized slurry of red mud in pregnant caustic liquor s.~'~utior.. The 33 preferred material of =abrication =or the vesse_ is mild steel of a ~hvckness o= about _.3 cm. ~= more) 3ependi.~.g on the pressur=_. =or =xample, an exemp':ary embodiment fcr prAENDE~ SHE'cT
use in the Bayer process has a height and diameter of 14 m. and about 3 m., respectively.
The cylindrical pressure vessel 12 has a dish-shaped closed upper end 16 and a plurality of vents 30 to permit release of accumulated gases that accumulate in the vessel 12 during operation. The vents 30 are operated manually as the need arises or they may be operated automatically, by a timing device. The cylindrical pressure vessel 12 is elongated as shown in FIG. 1 and preferably has a length-to-diameter ratio of between 2 and 6:1. In a preferred embodiment the length-to-diameter ratio approximates 4.5:1. Adjustments can be made to the length and width depending on the particular application desired.
As mentioned above, the vessel 12 also includes a bottom section 14 for accumulation and dewatering of solids. The bottom section 14 may be either hemispherical or conical, although conical is preferred for ease of fabrication. Preferably, the bottom section 14 has inclined sides as shown in FIG. l, and these inclined sides should make an angle between 30-60° from the horizontal. Ari angle of about 45° is preferred, because such a conical shape is easiest to fabricate, poses the acceptable height penalty, while providing for a good flow of solids from the vessel 12. The approximately 45° to the vertical angle promotes slippage of solids along the wall 14 into the discharge sump 20.
The discharge sump 20 mounted beneath the bottom section 14 is preferably cylindrical with the bottom closed by bottom plate 34. The bottom plate of the sump may also be fitted with a steady bearing for the lower end of the shaft of the raking/dewatering device. A solids discharge line 38 is also connected to the sidewall 42 of sump 20 and this line 38 is connected to the inlet of a discharge pump (not shown). The thickened solids are preferably withdrawn at a flow rate of less than about 1 m/sec, to minimize pressure drops.
In an upper region of the pressure vessel 12 is WO 94/26383 _ ~ ~ ~ ~ ~ ~ f 3 PCTICA94100246 mounted an elongated or deep feedwell 18 positioned to provide an annular space 19 between the feedwell 18 and the sidewall of the vessel 12. The letter S depicts an operating level for the :surface of a thickened slurry bed within the vessel, while the letter L depicts a typical operating level for li~~u:Ld in the vessel. The feedwell 18 has a bottom opening 46 a predetermined distance above the solids level S. The f~=_ec3well 18 also has a slurry feed inlet opening 27 to which is connected an inlet pipe 44, which includes a horizontal connector portion 43 and an elbow 45. Mounted wit::~in feed pipe 45 are a first flocculant injector 48 c_Lose to inlet opening 27 and a se~~ond flocculant injector 50 located upstream (relative to slurry flow) adjacent the elbow 45.
The upper portion oj: feedwell 18 includes an opening 26 which serves to dis~~h~~rge any gas that may be present and may also serve as <~ form of overflow weir permitting some return flow of clar:~fied liquid downwardly through th~= feedwell 18. It i:~ ~_ocated between vent 30 and overflow 39.
The feed slurry inlE~t 27 for the best mode of operating the device i:~ ~_ocated at a distance of about. 3 to 5 times the diameter of the feedwell 18 above the open bottom 46 and about 2 t=o 4 times the diameter from the top opening 26. The feedwel7_ should be designed to provide a sei=tling velocity of the flocs within a range of about. 20 to 200 m/hr and in a t~,rpical commercial installation, the feedwell 18 has a diameter of about 700 mm, a length of about 4 metres and the bottom opening 46 positioned at.
least 2 metres above the solids level S. Other locations are possible and may be advantageous under certain conditions .
I:n order to provide a proper collection and discharge of the thickened slurry bed, a raking mechanism 21 is provided. This is connected to an axial drive shaft 52 which is driven from the top of vessel 12 via an electric or hydraulic motor 63 and gear reducer 65.
WO 94!26383 ~ 1 PCTlCA94100246 At the lower end of drive shaft 52, a pair of axially spaced crossbars 22 and 23 are connected thereto. Mounted to these crossbars 22 and 23 are a series of raking members including inclined edge rakes 25, upper edge rakes 66, lower edge rakes 68 and a series of vertical stirring bars 56, 58, 60 and 62. A11 of these rotate with the shaft 52, providing mixing of the slurry, dewatering of the settled solids, and raking of the walls to ease the discharge through discharge line 38.
The level of the thicKened slurry is detected by means of pressure monitors mounted via connectors 24a, 24b and 24c in a sidewall of pressure vessel 12. Each detector unit comprises a rube portion 72 which extends through connector 24a, 24b, 24c into the interior of the pressure vessel 12. This l.ube 72 connects via an isolation valve 75, e.g. a gate or ball valve, to a further tube portion including a purging spool 76 connected to a flushing .liquid line 74. The entire assembly connects to a sen:~or 73 which determines the pressure. A typical senso~_~ is one sold by Rosemount, Inc.
of Eden Prairie, Minnesota under Model 1151DP/GP and 11446.
These sensors measure the pressure exerted against them at the point in the vessel where they are located.
The higher the solids content, the greater the pressure exerted. Therefore, the sensor can detect the presence of denser solids containing liquid as opposed to clear liquid floating above the denser material.
Specifically the pres:~ure displaces a remote diaphragm transmitting the measured pressure through a liquid filled system to the' sensor 73. The transmitted pressure displaces a sensing diaphragm creating a differential capacitance between the sensing diaphragm and capacitor plates. This differential capacitance is converted to an electrical signal which can be measured by a suitable instrument to provide information on pressure differentials to operating a moving plotter or the like.
~1603!~ ~;
WO 94/26383 ' PCT/CA94/00246 Four sensors are :installed, the first sensor mounted at ;?4a some distance above the expected maximum top level of t=he bed of settling :~ol.ids S as shown in FIG. 1. A
second pair of sensors i_s located at levels 24b and 24c which is in the vicinity of the operational preferred level S of settling solid~~ and midway between the upper and lower sensors, while the fourth sensor is located at level 24d some distance below the expected leve,~ of the top of the settling solids S. 4,Iith this arrangement, the signals that are transmitted to monitor the solids level in vessel 12 represent t:he difference between sensors at 24a and 24b as the upper detector and between sensors at 24c and 24d as the lower detector.
A typical reading f:rcm a moving plotter is shown in FIG. 7 for the upper detector and the lower detector. The numEerals 1-6 in FIG. 7 have the following significances:
1. Lower mud level. indication goes up.
Technical Field This invention relates to an apparatus and process for separating solids from liquid under pressure and more particularly to a pressurized decanter system for separating red mud from Bayer process liquor without need to depressurize the slurry.
Background Art The Bayer process, now more than 100 years old, extracts alumina from bauxite ore by contacting crushed or p~slverized bauxite with a hot solution of caustic soda, whose concentration of rdaOH is usually expressed as equivalent Na2C03, to di;asolve the aluminum hydroxides conta:.ined therein as sodium aluminate. This solution of high sodium aluminate concentration is called pregnant liquor. The remaining undigested insoluble residue, known as red mud, is separated from the solution, usually by filtration or sedimentation or both.
Red mud typically includes large quantities of finely divided solids resistant: to separation. Alumina manufacturing therefore creates a need for improved separation systems, particularly those that can rapidly separate large quantitiess of slurries in an efficient manner.
In this connection,. some preliminary attempts appear to have been made to use. pressurized settling devices in clarifying finely divided solids from slurries. U.S.
Patent No. 2,107,919 (Turner) appears to discuss a pressure digester placed between two blow off tanks. U.S.
Patent No. 4,994,244 (Fulford) states that separation of ra_d mud from the digested slurry can be carried out at a temperature below the boiling atmospheric temperature of t:he liquor phase of the slurry. U.S. Patent No. 5,080,803 (:Bagatto) discusses a process and apparatus for decanting suspensions at and above' the atmospheric boiling point of t:he suspension. The apparatus operates at atmospheric pressure.
21fi034~
,.. .. .. .... .. ....
.. .. . .. . . . . . ..
... . . . . . . ....
. . . . . . ...
. .. .
.".. .... 2 .. .. .. ...
While the foregoing references discuss attempts to increase separation efficiency of finely divided solids from slurries, there exists a need, particularly in the aluminum industry, for improved systems to carry out separation at high pressure and temperature.
Disclosure of the Invention The present invention relates to both an apparatus and process for separating solids suspended in an incoming pressurized liquid s7_urry.
The apparatus of: the invention includes an elongated, upright vessel of generally circular cross-section having a closed top end and a bottom sump for accumulating solids. A feedstock inlet is provided for feeding a liquid slurry into the vessel and a f~occulant injector is provided for injecting flocculant into the liquid slurry feedstock. The vesseal also_includes an outlet for discharging clarified liquid in an upper region thereof and an outlet in the bottom sump for drawing off separated solids. Other featui:es of the vessel include a means for detecting the Ieve:L of thickened slurry bed in the vesse'~.
and a raking/dewater:_ng device for slurry extending into the bottom sump.
In accordance w::th the present invention, the apparatus of above t;rpe is specia'~ly adapted for use in carrying out separat:_on at high pressure and temperature.
This includes a feedstock inlet system for receiving pressurized liquid s:.urry including an elongated cylindrical feedwell mounted axially in an upper region. of the vessel with an annular space between the feedwell and vessel wall, this feedwell having an open bottom, an opening in an upper region thereof and a feed inlet for the liquid slurry .Located in a side wall of the feedwell between the open bottom and upper opening.
The feedstock inlet into the feedweil is located a distance above the open bottom of the feedwell su~f'_cient to permit substantia:: f'~occulation of so'_ids and clarification of liqmid within the =eedwe_'~. Also, the AMENDED S~=~ ~
~1603~v oven bottom of the feeciwell v~s positioned above the surface of a thickened Slurry bed in the vesse~ a c=stance suffic=ent to permit c=_arified liquid emerg-~ng downwardlv from the bottom of the feedweil to separate _rom the floccu'~ated solids and travel upwardly in the annular ,,, space between t~:e feedwell and vesse'~ wa_ls to discharge through the upper outlet without substantially disturbing the thickened slurry bead. The outlet for discharging clarified liquor is adapted to operate under pressure, as is the outlet in the bottom of the sump.
Preferably the upper opening in the feedwell is located to permit a po._ti on of t:~e clan ified 1 i quid travelling upwardly th:=ough the annular space to enter the feedwell through the ot~ening in such a manner as to 1S provide an inverted chimney effect within the feedwell.
Thus ) the- portion of c l ar;~.fied l,;quid~ entering the- upper opening of the =eedwei:'_ _ravels downwardly through the f°eClWe l 1, mlX;ng Wlr..~_ <3n(~ dllllt~ng .'.:ie _:'lCOmlilg ~~?eC
si~r=y Wnlc.~. d=QS _~CCCL:latl0n. The upper Open;:lg 31SC
permits t:~e dvsengageme~nt of the accumulation of gas bubbles that would of:~e~r~rise hinder flocculation. anti settling.
The pressurized liquid slurry being fed tc t:~~e apparatus normally has a flocculant incorporated therei_~.
and this floccuiant is typically added by way of at least one injector mounted within an inlet pipe connected to the feed inlet of the feed~Nell. Typically, two injectors are used, the first being :Located adjacent the feed inlet of the feedwell and the second injector being located upstream from the first injector.
The elongated, upright pressure vessel of the invention is typically a cylindrical vessel of substantially uniform ~~ross-section. ~iowever, according to an alternative embodiment of this invention _~ is possible to use a vessel having a lower sector. of ~;arger cross-section: and a cylindrical upper sec~ior_ of sma'_~er cross-section.. __ is, cf course, necessary to have as ~~ow AMCi'JG~:: :~;; ;c=T
,_ as practical an averag~=_ upflow velocity of the separating clarified ,_i~uv-d i~ th~= zone v~.n which the flocculated soli ds are separating and fal~.ng downwardly =rom t:~e S lower end of the f?edw=11 toward the bed of thickened slurry, t:zereby hindering the downward passage of the solids as _y..t=a as possible. For t:zis reason, the vessel Ar'~~~~ c~
"'~ = 1 WO 94126383 216 0 3 4 ~ PCTlCA94100246 must have a relatively large diameter in this portion of its height. On the other hand, the portion of the vessel extending above the lower end of the feedwell does not have this velocity restriction and it has quite surprisingly been found that very clear overflow liquids containing as little as 25 mg/1 suspended solids can be obtained even in cases where the average upflow velocity of the separated liquid in the annular space between the feedwell and vessel is 20 to 25 m/h or higher. For this reason, the diameter of the upper portion of the pressure vessel can be considerably smaller than the lower portion of the vessel.
This provides important advantages in substantially lowering the costs of material for a pressure vessel and, furthermore, the relatively high velocity of the liquid travelling upwardly through the annular space between the vessel wall and feedwell considerably decreases scaling of the surfaces of the vessel.
The lower portion of larger cross-section can be spherical in shape or it may be in the form of a low, relatively fat cylinder with upper and lower conical portions, or a polyhedron, or a combination of these shapes. Preferably the maximum diameter of the lower section is at least 1.75 times the diameter of the smaller upper section.
The means for detecting the level of the thickened slurry bed within the vessel is preferably in the form of a series of pressure dif:Eerential detectors mounted in the cylindrical wall of the vessel. It is important that these not interfere with the settling of the thickened slurry bed and therefore should protrude as little as possible into the interior of the vessel.
Brief Description of the Drawincts FIG. 1 is a front view in section of the improved pressure decanter of the present invention.
FIG. 2 is a sectional view, partially broken away, of the improved pressure decanter of FIG. 1, taken along '~1603~~
line 2-2 i-~. - =G. 1.
- r. ,_ r ~ . _ ~ ,~ _ . = a r-a r 4, ~~ a _ m:. 3 .S a S_.__..OYla, ~__w ~;L t~lE'_ mDrJV~.~. C_ SSLi__ decanter of FI,~. _ taken along line _-3 in ~=G. _.
FIG. a is a schematic representation o~ a mounting ,, 3 for a _eve'_ indicator i_or vsse in the =mproved pressure decanter of ~TG~ ~.
FIG. 5 is a schc=matic representatior_ of an alternative corm of decanter vessel.
FIG. o' is a schematic representation of a still further form oz decanter vessel, and FIG. 7 is a graphical representation of settling in the improved pressure decanter of F.IG. _ measured 'revel detectors.
3est Modes =or Ca=rvi~cz Out =he =nvent~.or_ FIGS. 1-~ illustrate a preferred embodiment .~.L the pressure decanter-of the present invention Generally designated with the =e_erence number 10 '.'he pressure decanter 10 genera l ly :_nc l udes a cylindr ical pressur a vessel 12, a cr°_=°_ra.bl~r conical ~cttom sectior_ ';4, a closed upper end 15, a deep =eedwell 18 =or incoming pressurized slurry, and a sump 20 below the 'onical bottom section 14 to facilitate removal of solids under pressure from the decanter '~0. It also has ar_ upper out';et 39 _or discharging clariLied :Liquid under pressure. =urthermore, it includes a raking/d~~watering device 2inside the bottom section 14, a p.Lurality of mud level detectors 24 to determine the level of settled solids. The vessel 10 stands generally upri ght as shown in FIG . _ ar_d i s supported by legs 28.
The cylindrical pressure vessel 12 has an elongated cylindrical vessel wall of suf~icient strength and thickness to withstand t:~e pressures, temperatures and corrosiveness of the c~~ntents such as pressurized slurry of red mud in pregnant caustic liquor s.~'~utior.. The 33 preferred material of =abrication =or the vesse_ is mild steel of a ~hvckness o= about _.3 cm. ~= more) 3ependi.~.g on the pressur=_. =or =xample, an exemp':ary embodiment fcr prAENDE~ SHE'cT
use in the Bayer process has a height and diameter of 14 m. and about 3 m., respectively.
The cylindrical pressure vessel 12 has a dish-shaped closed upper end 16 and a plurality of vents 30 to permit release of accumulated gases that accumulate in the vessel 12 during operation. The vents 30 are operated manually as the need arises or they may be operated automatically, by a timing device. The cylindrical pressure vessel 12 is elongated as shown in FIG. 1 and preferably has a length-to-diameter ratio of between 2 and 6:1. In a preferred embodiment the length-to-diameter ratio approximates 4.5:1. Adjustments can be made to the length and width depending on the particular application desired.
As mentioned above, the vessel 12 also includes a bottom section 14 for accumulation and dewatering of solids. The bottom section 14 may be either hemispherical or conical, although conical is preferred for ease of fabrication. Preferably, the bottom section 14 has inclined sides as shown in FIG. l, and these inclined sides should make an angle between 30-60° from the horizontal. Ari angle of about 45° is preferred, because such a conical shape is easiest to fabricate, poses the acceptable height penalty, while providing for a good flow of solids from the vessel 12. The approximately 45° to the vertical angle promotes slippage of solids along the wall 14 into the discharge sump 20.
The discharge sump 20 mounted beneath the bottom section 14 is preferably cylindrical with the bottom closed by bottom plate 34. The bottom plate of the sump may also be fitted with a steady bearing for the lower end of the shaft of the raking/dewatering device. A solids discharge line 38 is also connected to the sidewall 42 of sump 20 and this line 38 is connected to the inlet of a discharge pump (not shown). The thickened solids are preferably withdrawn at a flow rate of less than about 1 m/sec, to minimize pressure drops.
In an upper region of the pressure vessel 12 is WO 94/26383 _ ~ ~ ~ ~ ~ ~ f 3 PCTICA94100246 mounted an elongated or deep feedwell 18 positioned to provide an annular space 19 between the feedwell 18 and the sidewall of the vessel 12. The letter S depicts an operating level for the :surface of a thickened slurry bed within the vessel, while the letter L depicts a typical operating level for li~~u:Ld in the vessel. The feedwell 18 has a bottom opening 46 a predetermined distance above the solids level S. The f~=_ec3well 18 also has a slurry feed inlet opening 27 to which is connected an inlet pipe 44, which includes a horizontal connector portion 43 and an elbow 45. Mounted wit::~in feed pipe 45 are a first flocculant injector 48 c_Lose to inlet opening 27 and a se~~ond flocculant injector 50 located upstream (relative to slurry flow) adjacent the elbow 45.
The upper portion oj: feedwell 18 includes an opening 26 which serves to dis~~h~~rge any gas that may be present and may also serve as <~ form of overflow weir permitting some return flow of clar:~fied liquid downwardly through th~= feedwell 18. It i:~ ~_ocated between vent 30 and overflow 39.
The feed slurry inlE~t 27 for the best mode of operating the device i:~ ~_ocated at a distance of about. 3 to 5 times the diameter of the feedwell 18 above the open bottom 46 and about 2 t=o 4 times the diameter from the top opening 26. The feedwel7_ should be designed to provide a sei=tling velocity of the flocs within a range of about. 20 to 200 m/hr and in a t~,rpical commercial installation, the feedwell 18 has a diameter of about 700 mm, a length of about 4 metres and the bottom opening 46 positioned at.
least 2 metres above the solids level S. Other locations are possible and may be advantageous under certain conditions .
I:n order to provide a proper collection and discharge of the thickened slurry bed, a raking mechanism 21 is provided. This is connected to an axial drive shaft 52 which is driven from the top of vessel 12 via an electric or hydraulic motor 63 and gear reducer 65.
WO 94!26383 ~ 1 PCTlCA94100246 At the lower end of drive shaft 52, a pair of axially spaced crossbars 22 and 23 are connected thereto. Mounted to these crossbars 22 and 23 are a series of raking members including inclined edge rakes 25, upper edge rakes 66, lower edge rakes 68 and a series of vertical stirring bars 56, 58, 60 and 62. A11 of these rotate with the shaft 52, providing mixing of the slurry, dewatering of the settled solids, and raking of the walls to ease the discharge through discharge line 38.
The level of the thicKened slurry is detected by means of pressure monitors mounted via connectors 24a, 24b and 24c in a sidewall of pressure vessel 12. Each detector unit comprises a rube portion 72 which extends through connector 24a, 24b, 24c into the interior of the pressure vessel 12. This l.ube 72 connects via an isolation valve 75, e.g. a gate or ball valve, to a further tube portion including a purging spool 76 connected to a flushing .liquid line 74. The entire assembly connects to a sen:~or 73 which determines the pressure. A typical senso~_~ is one sold by Rosemount, Inc.
of Eden Prairie, Minnesota under Model 1151DP/GP and 11446.
These sensors measure the pressure exerted against them at the point in the vessel where they are located.
The higher the solids content, the greater the pressure exerted. Therefore, the sensor can detect the presence of denser solids containing liquid as opposed to clear liquid floating above the denser material.
Specifically the pres:~ure displaces a remote diaphragm transmitting the measured pressure through a liquid filled system to the' sensor 73. The transmitted pressure displaces a sensing diaphragm creating a differential capacitance between the sensing diaphragm and capacitor plates. This differential capacitance is converted to an electrical signal which can be measured by a suitable instrument to provide information on pressure differentials to operating a moving plotter or the like.
~1603!~ ~;
WO 94/26383 ' PCT/CA94/00246 Four sensors are :installed, the first sensor mounted at ;?4a some distance above the expected maximum top level of t=he bed of settling :~ol.ids S as shown in FIG. 1. A
second pair of sensors i_s located at levels 24b and 24c which is in the vicinity of the operational preferred level S of settling solid~~ and midway between the upper and lower sensors, while the fourth sensor is located at level 24d some distance below the expected leve,~ of the top of the settling solids S. 4,Iith this arrangement, the signals that are transmitted to monitor the solids level in vessel 12 represent t:he difference between sensors at 24a and 24b as the upper detector and between sensors at 24c and 24d as the lower detector.
A typical reading f:rcm a moving plotter is shown in FIG. 7 for the upper detector and the lower detector. The numEerals 1-6 in FIG. 7 have the following significances:
1. Lower mud level. indication goes up.
2. Increase flocculant dosage.
Lower mud level indication goes down.
Lower mud level indication goes down.
3. Decrease underflow rate.
Lower mud level indication goes up.
Lower mud level indication goes up.
4. Upper mud level indication goes up (accumulation of mud) 5. Increase underflow rate to decrease mud level.
-Upper mud level goes down.
-Upper mud level goes down.
6. Lower mud level goes down.
-Mud inventory decreases.
It will of course, be appreciated that various other mechanisms are possible for measuring these differential pressures and other types of non-intrusive gauges may include those of ultrasonic sonar or radiation type (gamma gauge ) .
FIGS. 5 and 6 show two embodiments of the apparatus of the invention having a lower section of larger cross section and a cylindrical 'upper section of smaller cross section. Looking at FIG. 5, it includes a large spherical bottom portion 80 to the t~~p end of which is connected a cylindrical portion 81 of much smaller diameter. The feedwell 18 is primarily mounted within the small cylindrical portion 81 with the lower end of feedwell 18 projecting into the large sphere. The top end of feedwell 5 18 has an opening 47 which permits upward discharge of gases and a return flow of some of the clear liquid which travels up the annular space 19 between feedwell 18 and cylindrical member 81.
The lower spherical member 80 is sufficiently large 10 to permit separation of clarified liquid from flocculated solids as a discharge from the bottom outlet 46 such that the flocculated solids continue downwardly to collect on the surface of the solids S while the clarified liquid travels upwardly through the annular space 19.
15 A cylindrical sump 20 is connected to the bottom end of the sphere 80 and the solids discharge line 38 is connected to sump 20. A rotating rake member is connected to the bottom end of drive shaft 52 and this includes a horizontal portion 35, inclined portions 36- and vertical 20 portions 37 extending downwardly into the sump 20.
FIG. 6 shows a design basically similar to that of FIG. 5, the primary difference being that the sphere 80 of FIG. 5 has been replaced by a relatively fat spherical member having a central cylindrical portion 82 with inclined upper walls 83 and inclined lower walls 84.
Again, a sump 20 is connected to the lower end of the bottom inclined portion 84 and a rake member is connected to the lower end of drive shaft 52. This rake member includes a horizontal member 40, vertical members 41, inclined members 49 and vertical members 51 extending downwardly into the sump 20.
Having described the structure of the apparatus, its operation can now be understood with reference to the clarification of Bayer process slurry involving the separation of red mud solids from hot fresh pregnant Bayer process liquor still at approximately the same pressure and temperature as in the digestion process. Referring to 2~ 6034 ~
1-4, a Dr°_SSllr;Z!?C1 Stream G~ ~aVe~ JrCCeSS S~llrr'f ncluding red mud ar_c '=:~e pregnant ~.iquor !not shown;
enters thr Cllg.': ;.~1° t _ =pe 4''_ W.''ler e_.ri 1 t r eCei'JeS tWa ln~eCt10I1S ..~. tW0 St3geS Cf f1 OCCL:I ant _~'Om __rSt arid second injectors 48, S0. ?referably t:-~e flocculant used in an anionic sodium p~~lyacr-~rlate or similar flocculant suitable for sett'.~~.ng red mud derived from bauxite, suc:.
as that avai'~able =rpm Allied Co~~.loids, ~imited under the trademark ALCAR 500, diluted to a concentration of :'_ess than about l.Oo by weight. The minor portion 0-SOo, pre-ferably about 30°->, of the total amount of flocculant is added through t:~e second ir_jection aoint 50 which is located near the el bow 45 in t:~~e sl urr,,r ;.~.? et pipe a4 , near the h=ghest poi.~.t just after c:zarce in direct=:gin. At this point _._ t:ze _=.~_et pipe 44 maximum turbulence ccc',:rs.
The slurry slides downward in the inclined inlet pipe 44 through t:tis zone of maximum turbulence toward the =eed-well =8, and r°_Ceiwes by ~~.njection the major portion of _, the _;occu'~ar.=, bet.ween about 50% and about 1000, Drefer-ably about ?0°s, t:-~roug:~ the =first ='_occulant i:.ject:zr 43.
When the slurry is adjacent the entry to the feedwe_';, the velocity of t:ne slur=-y i s nat greater t:~~an about 1 m/sec _ The siurrv ?.nterS ~._'7e Leedwell lr3 Wner°_ 1t 15 ClreCteC
downwardly through =he extended elongated column of the feedwell with flocculation and separation occurring within the column until it reaches the discharge opening 40. At this point, the velccity and kinetic energy of the slurry is such that the flocculated solids continue downwardly to settle on the surface of the bed of settling solids S, while the clari'_ied liquid moves upwardly through annular space 19 without substantially disturbing the bed o. set-tl ;~ng solids . ?~s tn.e solids sett'~.e toward the bottom section 14, =:rev lose more and more of t:~ei= 1 iqui ~' con-tent, and degas_tion. is aided by rake 2= _:tated by shat=
32. 3y the =ime ~_:zey reach sump 20, _:~.ev are -east e.~.se and may be withdrawn through oisc barge 1_ne 39. The =_na_ dewateri~g cf sol_-a __cm ~__gu;~? :.s he;~ed by the s'_cw WO 941:L6383 rotation of the shaft 52 turning rake 21.
The apparatus of FIGS. 5 and 6 work in essentially the same manner as that of FIGS. 1-4, except that in the apparatus of FIGS. 5 and 6 the annular zone is much sma7.ler, resulting in a much greater flow rate of clarified liquid upwardly in the annular zone.
The following examples are meant to be illustrative of t:he practices of the invention and not intended to be limiting.
Example 1 An improved pressure decanter in accordance with FIGLTRES 1 - 4 was used for a two-month period. The feed slurry of red mud was obtained by extracting Australian bau~:ite in 180 g/1 caustic, expressed as NazC03, at 130-150°C. The resulting slurry of red mud contained from 50 t:o 90 g/L solids. During the test period, the slurry floored into the decanter at a rate of up to 225 cubic meters per hour equivalent to processing up to 42 tons per hour- of bauxite, depending on the alumina content. The rate' of addition of synthetic flocculant was varied around the target level of 120 g/ton of bauxite. The upward velocity of the liquor in the annulus between the feedwell and the exterior wall of the vessel was about 21 m/hr, and the solids content of the underflow exiting from the decanter was between 40 and 50%.
Example 2 The performance of the pressure decanter of the invention was compared with that of the conventional settlers operating at atmospheric and also with a deep settler operating at a temperature slightly above the atmospheric pressure boiling point of the liquid being separated, similar to that described in U.S. Patent No.
5, OE~O, 030.
The pressure decanter of the invention was found to handle a mud load greater by an order of magnitude than the other settlers and to provide an overflow (O'F) clarity better by a factor of 2 or more. The suspended WO 94126383 , PCTICA94100246 solids averaged 20-25 mg/L, compared with 200 mg/1 for the conventional settlers. The invention gave a higher content of solids in the underflow (U/F) at 42o compared with 30-32% in the conventional equipment.
-Mud inventory decreases.
It will of course, be appreciated that various other mechanisms are possible for measuring these differential pressures and other types of non-intrusive gauges may include those of ultrasonic sonar or radiation type (gamma gauge ) .
FIGS. 5 and 6 show two embodiments of the apparatus of the invention having a lower section of larger cross section and a cylindrical 'upper section of smaller cross section. Looking at FIG. 5, it includes a large spherical bottom portion 80 to the t~~p end of which is connected a cylindrical portion 81 of much smaller diameter. The feedwell 18 is primarily mounted within the small cylindrical portion 81 with the lower end of feedwell 18 projecting into the large sphere. The top end of feedwell 5 18 has an opening 47 which permits upward discharge of gases and a return flow of some of the clear liquid which travels up the annular space 19 between feedwell 18 and cylindrical member 81.
The lower spherical member 80 is sufficiently large 10 to permit separation of clarified liquid from flocculated solids as a discharge from the bottom outlet 46 such that the flocculated solids continue downwardly to collect on the surface of the solids S while the clarified liquid travels upwardly through the annular space 19.
15 A cylindrical sump 20 is connected to the bottom end of the sphere 80 and the solids discharge line 38 is connected to sump 20. A rotating rake member is connected to the bottom end of drive shaft 52 and this includes a horizontal portion 35, inclined portions 36- and vertical 20 portions 37 extending downwardly into the sump 20.
FIG. 6 shows a design basically similar to that of FIG. 5, the primary difference being that the sphere 80 of FIG. 5 has been replaced by a relatively fat spherical member having a central cylindrical portion 82 with inclined upper walls 83 and inclined lower walls 84.
Again, a sump 20 is connected to the lower end of the bottom inclined portion 84 and a rake member is connected to the lower end of drive shaft 52. This rake member includes a horizontal member 40, vertical members 41, inclined members 49 and vertical members 51 extending downwardly into the sump 20.
Having described the structure of the apparatus, its operation can now be understood with reference to the clarification of Bayer process slurry involving the separation of red mud solids from hot fresh pregnant Bayer process liquor still at approximately the same pressure and temperature as in the digestion process. Referring to 2~ 6034 ~
1-4, a Dr°_SSllr;Z!?C1 Stream G~ ~aVe~ JrCCeSS S~llrr'f ncluding red mud ar_c '=:~e pregnant ~.iquor !not shown;
enters thr Cllg.': ;.~1° t _ =pe 4''_ W.''ler e_.ri 1 t r eCei'JeS tWa ln~eCt10I1S ..~. tW0 St3geS Cf f1 OCCL:I ant _~'Om __rSt arid second injectors 48, S0. ?referably t:-~e flocculant used in an anionic sodium p~~lyacr-~rlate or similar flocculant suitable for sett'.~~.ng red mud derived from bauxite, suc:.
as that avai'~able =rpm Allied Co~~.loids, ~imited under the trademark ALCAR 500, diluted to a concentration of :'_ess than about l.Oo by weight. The minor portion 0-SOo, pre-ferably about 30°->, of the total amount of flocculant is added through t:~e second ir_jection aoint 50 which is located near the el bow 45 in t:~~e sl urr,,r ;.~.? et pipe a4 , near the h=ghest poi.~.t just after c:zarce in direct=:gin. At this point _._ t:ze _=.~_et pipe 44 maximum turbulence ccc',:rs.
The slurry slides downward in the inclined inlet pipe 44 through t:tis zone of maximum turbulence toward the =eed-well =8, and r°_Ceiwes by ~~.njection the major portion of _, the _;occu'~ar.=, bet.ween about 50% and about 1000, Drefer-ably about ?0°s, t:-~roug:~ the =first ='_occulant i:.ject:zr 43.
When the slurry is adjacent the entry to the feedwe_';, the velocity of t:ne slur=-y i s nat greater t:~~an about 1 m/sec _ The siurrv ?.nterS ~._'7e Leedwell lr3 Wner°_ 1t 15 ClreCteC
downwardly through =he extended elongated column of the feedwell with flocculation and separation occurring within the column until it reaches the discharge opening 40. At this point, the velccity and kinetic energy of the slurry is such that the flocculated solids continue downwardly to settle on the surface of the bed of settling solids S, while the clari'_ied liquid moves upwardly through annular space 19 without substantially disturbing the bed o. set-tl ;~ng solids . ?~s tn.e solids sett'~.e toward the bottom section 14, =:rev lose more and more of t:~ei= 1 iqui ~' con-tent, and degas_tion. is aided by rake 2= _:tated by shat=
32. 3y the =ime ~_:zey reach sump 20, _:~.ev are -east e.~.se and may be withdrawn through oisc barge 1_ne 39. The =_na_ dewateri~g cf sol_-a __cm ~__gu;~? :.s he;~ed by the s'_cw WO 941:L6383 rotation of the shaft 52 turning rake 21.
The apparatus of FIGS. 5 and 6 work in essentially the same manner as that of FIGS. 1-4, except that in the apparatus of FIGS. 5 and 6 the annular zone is much sma7.ler, resulting in a much greater flow rate of clarified liquid upwardly in the annular zone.
The following examples are meant to be illustrative of t:he practices of the invention and not intended to be limiting.
Example 1 An improved pressure decanter in accordance with FIGLTRES 1 - 4 was used for a two-month period. The feed slurry of red mud was obtained by extracting Australian bau~:ite in 180 g/1 caustic, expressed as NazC03, at 130-150°C. The resulting slurry of red mud contained from 50 t:o 90 g/L solids. During the test period, the slurry floored into the decanter at a rate of up to 225 cubic meters per hour equivalent to processing up to 42 tons per hour- of bauxite, depending on the alumina content. The rate' of addition of synthetic flocculant was varied around the target level of 120 g/ton of bauxite. The upward velocity of the liquor in the annulus between the feedwell and the exterior wall of the vessel was about 21 m/hr, and the solids content of the underflow exiting from the decanter was between 40 and 50%.
Example 2 The performance of the pressure decanter of the invention was compared with that of the conventional settlers operating at atmospheric and also with a deep settler operating at a temperature slightly above the atmospheric pressure boiling point of the liquid being separated, similar to that described in U.S. Patent No.
5, OE~O, 030.
The pressure decanter of the invention was found to handle a mud load greater by an order of magnitude than the other settlers and to provide an overflow (O'F) clarity better by a factor of 2 or more. The suspended WO 94126383 , PCTICA94100246 solids averaged 20-25 mg/L, compared with 200 mg/1 for the conventional settlers. The invention gave a higher content of solids in the underflow (U/F) at 42o compared with 30-32% in the conventional equipment.
Claims (12)
1. An apparatus for separating solids suspended in an incoming liquid slurry feedstock including an elongated, upright vessel of generally circular cross-section having a closed top end and a bottom sump for accumulating solids; a feedstock inlet for feeding a liquid slurry into said vessel; a flocculant injector for injecting flocculant into the liquid slurry feedstock; an outlet for discharging clarified liquid in an upper region of said vessel; an outlet in said bottom sump for removing separated solids; means for detecting the level of a thickened slurry bed in the vessel, and a raking/-dewatering device extending into said bottom sump, characterized in that the feedstock inlet is a system for receiving pressurized liquid slurry including an elongated cylindrical feedwell mounted axially in an upper region of said vessel with an annular space between the feedwell and vessel wall, said feedwell having an open bottom located below the clarified liquid outlet, an opening in an upper region thereof and a feedstock inlet for said liquid slurry feedstock located in a side wall of the feedwell between the open bottom and upper opening, said feedstock inlet being located a distance above the open bottom of the feedwell sufficient to permit substantial flocculation of solids and clarification of liquid within the feedwell and the open bottom of the feedwell being positioned above the surface of a thickened slurry bed a distance sufficient to permit clarified liquid emerging downwardly from the bottom of the feedwell to separate from flocculated solids and travel upwardly in the annular space between the feedwell and vessel walls to discharge through said upper outlet without substantially disturbing said thickened slurry bed, and said outlet is adapted for removing separated solids under pressure.
2. An apparatus as claimed in claim 1 characterized in that the upper opening in the feedwell is located to permit a portion of the clarified liquid travelling up through the annular space to enter the feedwell through the opening such as to provide an inverted chimney effect within the feedwell.
3. An apparatus as claimed in claim 1 characterized in that the vessel is a cylindrical vessel of substantially uniform cross-section.
4. An apparatus as claimed in claim 1 characterized in that the vessel comprises a lower section of larger cross-section and a cylindrical upper section of smaller cross-section.
5. An apparatus as claimed in claim 4 characterized in that the bottom of the feedwell extends into the larger lower section.
6. An apparatus as claimed in claim 5 characterized in that the larger lower section is spherical.
7. An apparatus as claimed in claim 5 characterized in that the larger lower section is substantially cylindrical.
8. An apparatus as claimed in claim 1 characterized in that the sump is a downwardly projecting substantially cylindrical section having a cross-section substantially smaller than the lower section of the vessel.
9. An apparatus as claimed in claim 4 characterized in that the diameter of the lower section is at least 1.75 times the diameter of the upper section.
10. An apparatus as claimed in claim 1 characterized in that the level detecting means are pressure differential detectors mounted in the cylindrical wall of the vessel.
11. An apparatus as claimed in claim 1 characterized in that the feedstock inlet system includes an inlet pipe connected to said feed inlet, said pipe including at least one flocculant injector mounted therein.
12. An apparatus as claimed in claim 11 characterized in that it includes two said flocculant injectors, the first injector located adjacent said feed inlet and the second injector located upstream from the first injector.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US059,445 | 1993-05-07 | ||
| US08/059,445 US5407561A (en) | 1993-05-07 | 1993-05-07 | Pressure decanter |
| PCT/CA1994/000246 WO1994026383A1 (en) | 1993-05-07 | 1994-05-06 | Improved pressure decanter |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2160346A1 CA2160346A1 (en) | 1994-11-24 |
| CA2160346C true CA2160346C (en) | 1999-09-28 |
Family
ID=22023000
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002160346A Expired - Lifetime CA2160346C (en) | 1993-05-07 | 1994-05-06 | Improved pressure decanter |
Country Status (13)
| Country | Link |
|---|---|
| US (1) | US5407561A (en) |
| EP (1) | EP0696225B1 (en) |
| KR (1) | KR100329711B1 (en) |
| CN (1) | CN1051244C (en) |
| AU (1) | AU681657B2 (en) |
| BR (1) | BR9406391A (en) |
| CA (1) | CA2160346C (en) |
| DE (1) | DE69401206T2 (en) |
| ES (1) | ES2096468T3 (en) |
| FI (1) | FI955329A (en) |
| GR (1) | GR3022334T3 (en) |
| HU (1) | HU215983B (en) |
| WO (1) | WO1994026383A1 (en) |
Families Citing this family (16)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6340033B2 (en) | 1999-03-15 | 2002-01-22 | Alcan International Limited | Transfer of shear-thinning slurries |
| CA2267677C (en) * | 1999-03-31 | 2006-09-19 | Np Industries Inc. | Fluid treatment system |
| SE520068C2 (en) * | 2000-03-01 | 2003-05-20 | Itt Mfg Enterprises Inc | Methods and apparatus for treating liquids |
| US6655531B1 (en) | 2000-05-23 | 2003-12-02 | Baker Hughes Incorporated | Pressure filtration device |
| AUPS224802A0 (en) * | 2002-05-10 | 2002-06-13 | Alcoa Of Australia Limited | Method for clarifying bayer process liquors |
| US7578930B2 (en) * | 2005-10-18 | 2009-08-25 | Aquashield, Inc. | Mobile water treatment system |
| DE102005053151A1 (en) * | 2005-11-04 | 2007-05-10 | Epuramat S.A.R.L. | Method and device for thickening sludge entrained in sewage |
| FR2934852B1 (en) * | 2008-08-06 | 2011-06-24 | Alcan Int Ltd | IMPROVEMENT TO THE BAYER PROCESS FOR PRODUCTION OF ALUMINA TRIHYDRATE, SAID PROCESS COMPRISING A STEP IN WHICH THE SURSATURATED LIQUEUR IS FILTERED AT HIGH TEMPERATURE BEFORE DECOMPOSITION |
| US8518268B1 (en) | 2009-10-23 | 2013-08-27 | Flocate Industries, Inc. | Method and apparatus for mobile water filtration |
| EP2886177A1 (en) * | 2013-12-20 | 2015-06-24 | Rio Tinto Alcan International Limited | Settler and method for separating clarified liquid from mineral slurries |
| FI125479B (en) | 2013-12-23 | 2015-10-30 | Outotec Finland Oy | Combined heater-decanter and method for increasing the density of the feed suspension |
| WO2018009512A1 (en) * | 2016-07-06 | 2018-01-11 | Gradiant Corporation | Solids handling in water treatment systems and associated methods |
| CA3014968A1 (en) | 2017-08-18 | 2019-02-18 | Canadian Natural Resources Limited | High temperature paraffinic froth treatment process |
| EP3730461A3 (en) | 2019-04-25 | 2020-11-25 | CWC Clear Water Clarification Technologies Inc. | Fluid treatment system |
| AT522689B1 (en) * | 2020-06-15 | 2021-01-15 | Andritz Delkor Pty Ltd | DEVICE AND METHOD FOR SEPARATING A SUSPENSION |
| CN114293935B (en) * | 2021-12-31 | 2024-03-26 | 重庆大学 | Three-phase separation pressure maintaining device and use method thereof |
Family Cites Families (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2355069A (en) * | 1941-08-13 | 1944-08-08 | Infilco Inc | Liquid treating apparatus and process |
| US3184065A (en) * | 1961-12-29 | 1965-05-18 | Shell Oil Co | Settler |
| US4278541A (en) * | 1978-03-14 | 1981-07-14 | Amstar Corporation | Separator employing an annular vertical feedwell with associated concentric annular baffle plate and method of using same to separate solids from liquids |
| US4274958A (en) * | 1978-10-10 | 1981-06-23 | Dorr-Oliver Incorporated | Flocculant distributor means for feedwell |
| US4226714A (en) * | 1978-12-27 | 1980-10-07 | The Anaconda Company | Thickener control system |
| US4348278A (en) * | 1980-10-31 | 1982-09-07 | Carl Caccia | Settlement tank condition monitoring system |
| FR2568489B1 (en) * | 1984-07-31 | 1990-03-23 | Alsthom Atlantique | TWO-STAGE CLARIFICATION PROCESS FOR LIQUID LOADED WITH SOLID MATERIALS |
| US4603000A (en) * | 1984-09-05 | 1986-07-29 | Fabcon Incorporated | Process and apparatus for flocculating and clarifying a solid-liquid slurry |
| US4999115A (en) * | 1985-08-19 | 1991-03-12 | Peterson Filters Corporation | Method and apparatus for use in separating solids from liquids |
| US5080803A (en) * | 1989-10-13 | 1992-01-14 | Alcan International Limited | Process for decantation of suspensions |
| OA09268A (en) * | 1989-10-13 | 1992-08-31 | Alcan Int Ltd | Process and apparatus for decantation of suspensions. |
| JPH03146101A (en) * | 1989-11-02 | 1991-06-21 | Yonden Eng Kk | Sludge discharge device for sludge settling tank |
-
1993
- 1993-05-07 US US08/059,445 patent/US5407561A/en not_active Expired - Lifetime
-
1994
- 1994-05-06 AU AU66427/94A patent/AU681657B2/en not_active Expired
- 1994-05-06 EP EP94914995A patent/EP0696225B1/en not_active Expired - Lifetime
- 1994-05-06 CN CN94192029A patent/CN1051244C/en not_active Expired - Lifetime
- 1994-05-06 WO PCT/CA1994/000246 patent/WO1994026383A1/en active IP Right Grant
- 1994-05-06 KR KR1019950704978A patent/KR100329711B1/en not_active IP Right Cessation
- 1994-05-06 BR BR9406391A patent/BR9406391A/en not_active IP Right Cessation
- 1994-05-06 HU HU9503124A patent/HU215983B/en unknown
- 1994-05-06 CA CA002160346A patent/CA2160346C/en not_active Expired - Lifetime
- 1994-05-06 DE DE69401206T patent/DE69401206T2/en not_active Expired - Lifetime
- 1994-05-06 ES ES94914995T patent/ES2096468T3/en not_active Expired - Lifetime
-
1995
- 1995-11-06 FI FI955329A patent/FI955329A/en not_active IP Right Cessation
-
1997
- 1997-01-22 GR GR960403450T patent/GR3022334T3/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| WO1994026383A1 (en) | 1994-11-24 |
| EP0696225A1 (en) | 1996-02-14 |
| EP0696225B1 (en) | 1996-12-18 |
| AU6642794A (en) | 1994-12-12 |
| HU215983B (en) | 1999-03-29 |
| BR9406391A (en) | 1996-01-16 |
| FI955329A0 (en) | 1995-11-06 |
| US5407561A (en) | 1995-04-18 |
| AU681657B2 (en) | 1997-09-04 |
| CA2160346A1 (en) | 1994-11-24 |
| ES2096468T3 (en) | 1997-03-01 |
| KR100329711B1 (en) | 2002-08-13 |
| CN1051244C (en) | 2000-04-12 |
| DE69401206D1 (en) | 1997-01-30 |
| GR3022334T3 (en) | 1997-04-30 |
| HUT76198A (en) | 1997-07-28 |
| HU9503124D0 (en) | 1995-12-28 |
| FI955329A (en) | 1995-11-06 |
| DE69401206T2 (en) | 1997-04-24 |
| CN1122581A (en) | 1996-05-15 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKEX | Expiry |
Effective date: 20140506 |